M42 and M43 – The Orion Nebula, Fish's Mouth, and De Mairan's Nebula
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The Great Orion Nebula, also known as M42 (Messier 42), is the brightest diffuse nebula in the night sky and can be observed with the naked eye even under moderately challenging conditions. It is located in the constellation Orion, south of Orion’s Belt. Its distance from Earth is just over 1,300 light-years, making it the nearest stellar nursery to our region of the Universe. The diameter of this luminous cloud of cosmic gas and dust is approximately 30 light-years.
This nebula is one of the most popular objects of observation for both amateur and professional astronomers. It is part of a vast complex of nebulae known as the Orion Molecular Cloud. Within M42, protoplanetary disks, brown dwarfs, turbulent flows of vast amounts of gas, and photoionization effects can be observed.
The constellation of Orion, within which the Great Orion Nebula can be observed, is one of the prominent winter sky constellations. The photograph below, taken in my garden on January 18, 2021, at 8:30 PM, shows the southern part of the celestial sphere, featuring Orion and its surroundings:
The figure of Orion was placed in the sky by the ancient Greeks. In their mythology, Orion was considered one of the greatest hunters—he could move silently and even walk on water. He fell in love with the Pleiades, whom he still chases across the sky to this day as the star cluster M45. Orion met his end from the sting of a scorpion sent by the goddess Artemis. Since then, the constellations of Orion and Scorpius Scorpius lie on opposite sides of the sky. Even his loyal hunting dogs, Sirius and Procyon, were placed in the sky as the brightest stars of the constellations Canis Major (α Canis Majoris) and Canis Minor (α Canis Minoris).
Orion is a striking figure in the celestial sphere, containing many bright stars. Observations of the constellation are possible even from urban areas.
Interestingly, in the case of Orion, the alpha star (α) is not the brightest—this title belongs to Beta (β), or Rigel. Alpha, the second-brightest star, is Betelgeuse, a red supergiant located about 600 light-years away. If Betelgeuse were placed in the position of our Sun, its surface would extend roughly to the orbit of Jupiter. As seen, the color of Betelgeuse is distinctly redder than most other stars, and the star is likely nearing the end of its life cycle, expected to explode as a supernova in the astronomical future. Near Betelgeuse, in the position representing Orion’s other shoulder, is Gamma (γ), known as Bellatrix. Lambda (λ) Orionis is a multiple star system. Below Betelgeuse and Bellatrix (further south) lie the three bright stars forming Orion’s Belt: Delta (δ), Epsilon (ε), and Zeta (ζ) Orionis, named Mintaka, Alnilam, and Alnitak, respectively. Between the Belt and Beta (Rigel) and Kappa (Saiph) lies Orion’s Sword, where the Great Orion Nebula can be observed even with binoculars. It is illuminated from within by young stars that form the Trapezium Cluster, designated as Theta (θ). Slightly below, Iota (ι) Orionis, or Hatysa, can be found.
Near Orion, we can observe the northern regions of the constellation Eridanus Eridanus, which can never be fully visible from our latitude. Beta of this constellation is Cursa, while at the opposite, invisible end lies Alpha, or Achernar. One must not forget the Hyades—this open star cluster is located in Taurus Taurus. Alpha Tauri, also known as Aldebaran, is not part of the Hyades. Above Orion, you can spot Tianguan ζ Tau, which serves as a guidepost for locating the Crab Nebula M1.
Capturing images of the night sky no longer requires specialized equipment. With proper techniques, even modern smartphones can suffice. As evidence, I present Photo 2, taken on March 17, 2021, from my garden using a Xiaomi Redmi Note 8 Pro smartphone equipped with a modified version of the GCam app. Alongside the raw photograph, I’ve included a version annotated based on Bayer’s Uranometria. The full title of this work is Uranometria: omnium asterismorum continens schemata, nova methodo delineata, aereis laminis expressa, completed in the early 17th century. This allows us to see how the figure of Orion was imagined in the past.
While the Orion Nebula itself can be easily spotted with the naked eye as a faint patch of light, more detailed observations reveal the full beauty of this celestial object.
Observations
January 31, 2019, around 9:30 PM – Zaborze (Poland)
suburban conditions, moderate light pollution
It was not an especially cold night, with temperatures only a few degrees below freezing. The clear, moonless sky (a few days before the new moon) encouraged me to attempt some astrophotography.
The main object visible in the photograph is the Great Orion Nebula, or M42. It is a nearly spherical cloud of gas and dust containing numerous young stars, some of which have protoplanetary disks. Under appropriate conditions, its brightest regions can be observed even with the naked eye as a fuzzy, star-like patch, though binoculars can be helpful. Long-exposure photographs reveal the nebula’s delicate pink hue, illuminated from within by many young stars, including those within the Trapezium Cluster (the brightest area within the nebula). Slightly above M42 is M43, De Mairan’s Nebula, which surrounds the star ν Ori. The two objects are separated by a dark cloud of cosmic material known as the Fish's Mouth. Moving further upward, you encounter a complex of three nebulae: NGC 1977, NGC 1973, and NGC 1975, with the blue giant 42 Ori located within. The color of these nebulae is distinctly more bluish, especially when compared to M42 and M43. Besides these nebular objects, note the open clusters NGC 1980 and NGC 1981. The first is somewhat closer to the Solar System than the other objects and includes ι Ori, or Hatysa—a star located at the southern end of the asterism often referred to as Orion’s Sword. Using this star’s position is the easiest way to locate the other objects. NGC 1981 is located at the northern end of the Sword and, due to its loosely spaced stars, is best observed at low magnifications.
In my opinion, observing deep-sky images provides a wonderful sense of connection with the surrounding universe and helps gain a broader perspective.
March 10, 2021, around 8:00 PM – Jaworzno (Poland), garden
urban conditions, high-level light pollution
This time, I wanted to try photographing the nebula from an urban area with a very high level of light pollution. The result can be seen in Photo 4.
Unfortunately, the city’s light glow made the nebula nearly invisible. Only the use of a CLS filter made practical observation possible. This type of filter blocks the wavelengths of light emitted by mercury and sodium lamps (as well as other artificial light sources), which largely contribute to light pollution. However, it allows the transmission of wavelengths emitted by many deep-sky objects: doubly ionized oxygen lines (496 and 501 nm), the hydrogen-beta line (486 nm), and the deep red hydrogen-alpha line (656 nm). Naturally, using the filter required longer exposure times, but it enabled much more detailed visual observations of the nebula and its photography. The color of M42 appears slightly too red—this is likely due to the white balance settings, which did not match the filter used. In future attempts, I plan to use a custom white balance adjusted to the filter’s characteristics.
Photo 1 Parameters:
- Total exposure time: 10s (single shot)
- Panasonic dmc-fz7
- ISO: 400
- Mount: photographic tripod
Photo 2 Parameters:
- Total exposure time: 3 minutes
- Xiaomi Redmi Note 8 Pro + Gcam
- ISO: ?
- Mount: photographic tripod
Photo 3 Parameters:
- Total exposure time: 15 minutes (stack of 15 RAW frames at 60s each, using an appropriate number of dark, bias, and flat frames)
- Canon EOS 300D
- ISO: 3200
- Lens: zoom type (used at fmax = 250mm)
- A filter was used to reduce the effects of artificial light pollution and atmospheric glow
- Mount: equatorial mount with tracking, aligned using the drift method and controlled by a custom-built system.
Photo 4 Parameters:
- Total exposure time: 48 minutes (stack of 34 RAW frames at 85s each, using an appropriate number of dark, bias, and flat frames)
- Canon EOS 60D
- ISO: 2000
- Lens: zoom type (used at fmax = 250mm)
- A filter was used to reduce the effects of artificial light pollution and atmospheric glow
- Mount: equatorial mount with tracking, aligned using the drift method and controlled by a custom-built system.
- Autoguiding
Marek Ples